ASCII Spirals in Haskell

Spirals.hs

type Elem = [String]

width :: Elem -> Int
width e
  | (c:_) <- e = length c
  | otherwise = 0

height :: Elem -> Int
height = length

above :: Elem -> Elem -> Elem
above c1 c2 = widen w c1 ++ widen w c2
  where w = max (width c2) (width c1)

besides :: Elem -> Elem -> Elem
besides c1 c2 = zipWith (++) (heighten h c1) (heighten h c2)
  where h = max (height c1) (height c2)

widen :: Int -> Elem -> Elem
widen = map . (\ w l -> take w $ l ++ repeat ' ')

heighten :: Int -> Elem -> Elem
heighten w c = trim $ take w $ c ++ repeat ""
  where trim c = widen (width c) c

display :: Elem -> IO ()
display = putStrLn . unlines

spiral :: Int -> Int -> Elem
spiral n dir
  | 1 <- n = corner
  | otherwise =
    case dir of
      0 -> (corner `besides` row) `above` (sp `besides` space)
      1 -> (sp `above` space) `besides` (corner `above` col)
      2 -> (space `besides` sp) `above` (row `besides` corner)
      3 -> (col `above` corner) `besides` (space `above` sp)
  where
    sp = spiral (n-1) ((dir + 3) `rem` 4)
    row = [replicate (width sp) '-']
    col = replicate (width sp) ['|']
    space = [" "]
    corner = ["+"]

main = display $ spiral 10 0

Sample output -

+---------
|         
| +-----+ 
| |     | 
| | +-+ | 
| | + | | 
| |   | | 
| +---+ | 
|       | 
+-------+ 

Rewriting the _terrible_ code example from the official Scala book! - https://www.cs.helsinki.fi/u/wikla/OTS/Sisalto/examples/html/ch10.html#sec14